Merge pull request clj-time#143 from siscia/periodic-add

Periodic add

Author: michaelklishin

src/clj_time/periodic.clj

@@ -1,12 +1,20 @@
 (ns clj-time.periodic
-  (:require [clj-time.internal.fn :as ifns]
-            [clj-time.core :as ct])
+  (:require [clj-time.core :as ct])
   (:import [org.joda.time DateTime ReadablePeriod Period]))
 
 (defn periodic-seq
-  "Returns an infinite sequence of date-time values growing over specific period"
-  [^DateTime start ^ReadablePeriod period-like]
-  (let [^Period period (.toPeriod period-like)]
-    (map (fn [^long i]
-         (ct/plus start (.multipliedBy period i)))
-       (iterate inc 0))))
+  "Returns a sequence of date-time values growing over specific period.
+  The 2 argument function takes as input the starting value and the growing value,
+  returning a lazy infinite sequence.
+  The 3 argument function takes as input the starting value, the upper bound value,
+  and the growing value, return a lazy sequence."
+  ([^DateTime start ^ReadablePeriod period-like]
+   (let [^Period period (.toPeriod period-like)]
+     (map (fn [i]
+            (ct/plus start (.multipliedBy period i)))
+          (iterate inc 0))))
+  ([^DateTime start ^DateTime end ^ReadablePeriod period-like]
+   (let [^Period period (.toPeriod period-like)]
+     (take-while (fn [^DateTime next]
+                   (ct/before? next end))
+                 (periodic-seq start period-like)))))

test/clj_time/periodic_test.clj

@@ -33,3 +33,16 @@
          d1 (second uds)
          d2 (nth uds 2)
          d3 (nth uds 3))))
+
+(deftest test-limited-periodic-sequence
+  (let [d0 (date-time 2014 1 31)
+        d1 (date-time 2014 2 28)
+        d2 (date-time 2014 3 31)
+        d3 (date-time 2014 4 30)
+        uds (periodic-seq d0 d3 (months 1))]
+    (are [a b] (= a b)
+         d0 (first uds)
+         d1 (second uds)
+         d2 (nth uds 2))
+    (are [i] (thrown? IndexOutOfBoundsException (nth uds i)) 3)))
+